Early computer motherboards implemented a single voltage level, typically 5 volts, for use by the processor, chipset, and other components on the motherboard. As technologies for semiconductors scale down, designers scale voltage levels to reduce heat generation and power consumption. For instance, the voltages for power rails throughout the motherboard reduced from 5 volts to 3.3 volts. Newer components such as chipsets and processors operate at even lower voltages by using what is called a dual voltage, or split power rail design, which allows the internal components to operate at different voltage levels than interfaces for external components.
The transition from a single voltage level to multiple voltage levels led to the necessity of multiple voltage regulators on modern motherboards. The voltage regulators reduce the 5 volts signal to those voltages typically utilized by components such as 3.3 volts, 2.8 volts, 2.5 volts, 1.8 volts, and/or 1.5 volts. However, designers found that the increasing complexity of the platform design has led to conflicts between and within the components if the power rails are not established in a particular sequence.
The current solution for satisfying a design-dependent sequence requirement is to design logic such as discrete logic or to program programmable logic devices (PLDs) to coordinate powering of the power rails. The logic powers the power rails in accordance with the sequence requirement by enabling voltage regulators in a pre-determined order to assure that the platform operates properly. For example, sequence requirements of modern platforms typically require the power rails of a processor's core to be established after establishing the power rails for the processor's input-output (I/O) interface so the logic transmits an enable signal to the voltage regulator for the processor's I/O interface, awaits a power good signal from the voltage regulator, which is indicative of stabilization of the power rails for the processor's I/O interface, and then enables the voltage regulator for the processor's core. Sequence requirements of modern platforms typically require the power rails for a chipset core to be established before an I/O interface for the chipset.
Motherboards may include one or more discrete logic devices and/or PLDs to implement the pre-determined order for power rails. The problems with the current solution are that adding such logic devices adds cost to the design and consumes valuable board space to mount and to form connections between the logic device(s) and the voltage regulators for the platform. Further, designers spend a significant number of man-hours designing, programming, and debugging the logic.